Sclerotinia Blight

Sclerotinia blight is a fungal disease of alfalfa, beans, cabbage and other cole crops, kiwifruit, peanuts, soybeans, sunflowers, sweet potatoes, and tomatoes.

Bush bean infected with Sclerotinia blight (Rasbak) Public Domain

The Sclerotinia sclerotiorum fungus is found in the soil and on infected seeds. It can cling to shoes, garden tools, and wheelbarrow wheels. And once it’s in your soil, you may never get rid of it.


This insidious pathogen infects your plants long before you see any symptoms, but it’s a good idea to know what to look for.


Sclerotinia blight symptoms

Plant wilting and yellowing of side and main branches are the first signs of Sclerotinia blight, usually occurring mid to late-season. Closer inspection of the bottom of the plant will show white fluffy mycelium on the stem and soil surrounding the plant. If you were to open up this blighted stem, you would see black bits, called sclerotia, that may be as large as mouse droppings. Those sclerotia are the fungal intruder.

Pole bean infected with Sclerotinia blight (Rasbak) Public Domain

This fluff is easiest to see early in the morning when it is likely to be covered with dew. It may not be visible in the afternoon because the sun dries it out. If the mycelium is easy to see in the afternoon, it is probably southern blight.


Plants infected with Sclerotinia blight will develop sunken, light-colored, elongated lesions. If you were to roll an infected stem between your fingers, the tissue would fall away in something called shedding. This occurs because everything except the vascular tissue is rotting. Affected branches die and turn dark brown.


Sclerotinia management

Like other blights, Sclerotinia blight is easier to prevent than cure. Use these tips to avoid getting the disease in your garden in the first place:

• clean garden tools after each use with soap and water or a bathroom disinfectant
• select varieties that ripen early in the season
• use resistant seeds and seedlings that are certified disease-free
• space plants properly to allow for good airflow
• protect vines and stems from damage
• irrigate deeply, allowing the soil to dry out between waterings
• avoid overhead watering

If an infection occurs, diseased plants should be removed immediately and completely and thrown in the trash. They should not be added to the compost pile. Fungicides rated for use against Sclerotinia blight can be used as a preventative measure, but they won’t cure the disease once it takes hold. These fungi can remain viable in the soil for several years, so crop rotation is not helpful.

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So get out there and keep your plants healthy!